The present invention relates to a method for adjusting a register in a web-fed rotary printing press. An actual value of a web tension is determined and is compared to a reference value.
A device is known from DE 295 01 373 U1, wherein two image adjustment rollers are arranged between the second and third double printing groups of a rotary printing press having four double printing groups.
The image adjustment rollers are seated, freely rotatable, on pivotable levers. A reading head for scanning register marks, which is connected with an adjusting unit, is arranged downstream of the fourth double printing group. This adjusting unit provides signals by a comparison of a reference with an actual value. An actuating unit is acted upon for putting the image adjustment rollers against something in response to these signals.
DE 26 13 600 A1 discloses a regulation of the number of revolutions of a printing press, wherein guide rollers are regulated as a function of the web tension.
The object of the present invention is directed to providing a method for adjusting a register.
In accordance with the present invention, this object is attained by determining an actual value of a web tension and comparing it with a reference value. If a deviation between the two exceeds a permissible tolerance, the number of revolutions or the angular position of one of the cylinders is changed.
The advantages which can be realized by means of the present invention reside, in particular, in that available drive motors of the cylinders, or of the printing groups, are used for adjusting the color register. Image-scanning sensors are also not required. The web tension, which is detected by means of simply constructed sensors, is used as the input value for the adjustment.
It is known that noticeable register deviations in the running direction of a web can occur, mainly at roll changes, but also during the running production, which register deviations disappear only after an extended running time, if the register is not adjusted.
The causes of these register deviations are web tension changes in the web as the web passes between the individual printing positions, for example when the web is passing through the device for applying adhesive (2 thicknesses of paper plus the adhesive foil), or when changing the water application.
So-called image track adjusting devices are employed for compensating the fan-out tendencies of the web in eight-element towers.
If now, for example, the small image track adjusting roller in the center of the paper web is prepared, for example by means of wire strain gauges at the support arm in such a way that it can function as a force sensor, the result is a simple possibility for affecting the behavior of the color register of the print unit. It is only necessary to insure that the force on the web at the small image track wheel is maintained constant during production. It is unimportant in this instance how great the force is. It is only necessary to generate a sufficiently large measuring signal, for example 1 to 10 V, or 4 to 20 mA by means of the placement.
The force is maintained constant by the rotation of the respective printing groups. Constant web tension, along with the same wetting, results in the same color register.
Since only the relative deviation of the force is important for the register adjustment, it is possible to employ this type of adjustment with all web tensions sufficient for the production, with all papers used and at all production speeds.
It is only necessary that the printer releases the reference value for the comparing force signal, once its quality stage has been reached, for example by closing the waste shunt.